The future of telecommunications promises continuing advances in wireless and optical fiber communication technologies (among many others), culminating in the delivery of these technologies directly into people's private homes. With the impending introduction of equipment borne of these new technologies (better telephones, fax machines, computers and new types of machines not now dreamt of), a need is rapidly developing for sophisticated power conversion equipment to be located in the home to provide electric power to the equipment. The need is created because wireless communications and fiber-to-the-home interfaces cannot presently support distribution of their own electrical power.
Historically, public telephone systems have proven to be inexorably reliable. People have understandably come to expect that their ability to carry on electronic communication will be uncompromised, even if a power outage suddenly extinguishes every light in the house. Therefore, future power conversion equipment (or "power supplies") destined to provide power to residential telecommunications equipment will, most likely, require a battery reserve system for providing reserve power to the equipment in case commercial power is interrupted.
Current designs for power conversion systems for residential telecommunications equipment are based on a partitioned architecture, having both a central uninterruptible power supply ("UPS") stage and one or more peripheral converter stages. Ideally, the central UPS stage is mounted in a location that is protected from the elements (such as a garage, closet or attic) A peripheral converter stage is associated with each piece of telecommunications equipment to be powered, often being incorporated within the main chassis of the equipment itself. A bus runs throughout the house to couple the peripheral converter stage(s) to the central UPS stage.
The central UPS stage includes a primary converter for converting commercial power (120 volt, 60 Hertz AC in the United States) to an elevated distribution voltage (typically ranging from 24 to 48 volts DC, and often being 28 volts DC). The distribution voltage is elevated to increase bus efficiency. The central UPS stage further includes a battery boost converter (or boost converter) coupled to the battery reserve system (or battery) that boosts the battery voltage to the same distribution voltage. Mode switching circuitry within the central UPS stage alternatively couples either an output of the primary converter to the peripheral stage(s) (when the commercial power functions) or an output of the boost converter to the peripheral stage(s) (when the commercial power has failed).
Each peripheral stage includes a DC/DC converter that converts (usually decreases) the distribution voltage to an output voltage corresponding to that required by the telecommunications equipment to be powered.
One limitation of this type of partitioned power conversion system is that the efficiency of the system suffers greatly under light load conditions. The telecommunications equipment designed to be powered by such systems often employ advanced power management techniques, such as intermittent sleep modes, that continually lighten the load on the power conversion system. Even though the converters of the first and second stages may employ switching regulators to maximize efficiency under heavier loads, today's regulators still tend to be highly inefficient under light load conditions. For instance, at about ten percent of rated load capacity, it is not unusual for a partitioned power conversion system to attain no more than forty-five to fifty percent efficiency. Under these conditions, losses in the power conversion system may in fact exceed the power dissipated in the telecommunications equipment.
Further, when commercial power fails and the power conversion equipment is forced to draw its power from the battery, the boost converter introduces its own inefficiencies, compounding the problem of overall system inefficiency under light load conditions.
What is needed in the art is a system and method for increasing the efficiency of partitioned power conversion systems of the type described above under light load conditions.